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Appreciation ・ Intermediate
An intermediate quiz on sori types (koshi-zori, saki-zori, kyo-zori) and reading the era — koto (old sword) vs. shinto (new sword) — from the blade's overall shape (sugata). See the /appreciation sori and era comparison diagrams.
Koshi-zori has its deepest curvature near the base (koshi) of the blade, a hallmark of Heian and Kamakura period koto (old swords). Deepest near the tip is saki-zori, deepest at center is kyo-zori, and minimal curvature is mu-zori. Compare the shapes on the /appreciation sori diagram.
Saki-zori (deepest near the tip) is characteristic of late and final Muromachi period uchigatana. Heian and Kamakura tachi feature koshi-zori, and Edo shinto blades tend toward shallower sori overall. Check the saki-zori shape on the /appreciation diagram.
Koto blades from the Heian and Kamakura periods feature deep koshi-zori suited for mounted combat. In the Edo period, with stable governance and a shift to foot-soldier use and iaijutsu, shinto blades generally became shallower in sori. Shinto having deeper sori than koto is the reverse of the actual trend; sori was not eliminated entirely. See the /appreciation era comparison diagram: 'koto: 腰反り深い' vs. 'shinto: 反り浅い'.
The Nanbokucho period saw prolonged warfare, and blades of this era are characteristically grand, wide, thin in kasane, and imposing. The /appreciation era comparison diagram labels nanbokucho as '豪壮・幅広' (grand and wide). Slender with shallow sori describes Edo shinto, short and narrow describes kodachi or wakizashi types, and no sori describes the straight chokuto.
Kyo-zori has its deepest curvature near the center of the blade — between the koshi-zori (deep near base) and saki-zori (deep near tip) types. The nakago root is part of the tang, not the blade body, and the positions near kissaki or yokote correspond to different sori types. Confirm the kyo-zori shape on the /appreciation sori diagram.